Electric switch



y 1933- s. s. GREEN 1,920,031

ELECTRIC SWITCH Filed May 26, 1930 2 Sheets-Sheet l A TT'OVRNEY 5 July25, 1933- s. s. GREEN ELECTRIC SWITCH Fi1 ed May 26, 1930 2 SheetsShe et2 INVENTOR ATTORNEY Patented July 25, 1933 UNITED STAT it STANLEY S.GREEN, OF FAYETTE, INDIANA, ASSIGNOR T0 DUNCAN ELECTRIC MANUFACTURINGCOMPANY, OF LA FAYETTE, INDIANA, A CORPORATION OF ILLINOIS ELECTRICSWITCH Application filed. May 26,

My invention relates to controllers for electric circuits and is ofparticular utility in connection with structures forming the subjectmatter of my copending application Serial N 0. 285,114, filed June 13,1928, though my invention is not to be limited to this use. In my saidcopending application I have disclosed an electric circuit controllerwhich is inclusive of a body of electric current conducting material,such as mercury,

that is normally contained in the bore or,

passage of a conduit made of insulating material. This currentconducting liquid serves to electrically connect two electrodes of theassociated circuits, when the device is in circuit closing position.When there is an abnormal flow of current through the device, the liquidconductor, or a sufiicient portion of it, is expelled to break theelectrical connection between the electrodes and thereby open thecircuit and guard the translating devices within the circuit. The liquidconductor and associated electrodes and parts thus constitute a circuitprotecting switch.

My present invention has for its general object the formation of aswitch structure which is simple and yet strong enough to withstand theviolence which attends its operation. Another object is to provide anair tight envelope for the switch, so protected from the arcing andmechanical shocks originating within the switch as to be unaffected bythem. It also aims to provide a generous flash-over distance within theswitch to minimize destructive arcing. Still another object is toprovide a controller having the proper time-lag characteristics uponautomatic operation.

In carrying out my invention, I reenforce the conduit of insulatingmaterial with a metallic band and support which fasten it firmly inspaced interior relation to the container. I desirably provide suchcontainer in the form of two mating shells or cups of insulatingmaterial clamped together with a sealing material or cement therebetweenand arranged to beimperforate to the outer air. Reenforcing andsupporting means on the conduit of insulating material are desirabl1930. Serial N0. 455,679.

confined to a zone intermediate the ends of the conduit, therebyproviding greater flashover distance of the controlled current aroundthe conduit and through the metal support thereof and such reenforcingand supporting means for the insulating conduit as well as one or moreof the electrodes are given a large volume of metal and extendedradiating surface to cause as small a time lag as desired in theautomatic operation of the device. The arcing distance betweenelectrodes when the circuit is broken is made ample to prevent anycontinuation of such arcing through the insulating conduit and allarcing is removed from the walls of the container a sutficient distanceto prevent injury of such walls by the arcing. One of the electrodes isalso preferably extended to provide an arc shield for the container.

The invention has other characteristics and will be more fully explainedin connection with the accompanying drawings, in which Fig. 1 is a frontelevation of the preferred formof circuit controller shown in normalcircuit closing or on position; Fig. 2 is a side elevation of the deviceas it appears in Fig. 1; Fig. 3 is a front elevation partially insection, the removable front section of the enclosing casing beingomitted; Fig. 4 is a view, somewhat similar to 30 Fig. 3, but showingthe controller in the off position and illustrating parts in ele vationthat appear in section in Fig. 3; Fig. 5 is a sectional view on line 55of Fig. 1, but with the conduit of insulating material and itssupporting structure removed so as to show the iron feed tube and itssupport clearly; Fig. 6 is a view similar to Fig. 5 but with the conduitof insulating material fastened in place in the housing, such conduitand its supporting structure being shown in cross section; Fig. 7 is a.sectional view on line 77 of Fig. 1 with the insulating conduit and itssupporting structure removed to show more clearly the upper electrodeand its support; Fig. 8 is a. view partly in section of a modified formof insulating conduit and its support; and Fig. 9 is a view partly insection of still another modification of the insulating conduit and itssupport.

In the forms of the invention illustrated, the casing is formed ofinsulating material, such as moulded bakelite or a similar mouldedmaterial having a phenolic resin base, excepting for the bolts, screwsand the anchorages that are united therewith. This casing is inclusiveof the front half or removable cup shaped section or shell 1 and therear half or removable cup shaped section or shell-2. These casingsections are clamped snugly together, as by means of the metallic bolts3 which pass through external ears 3 and 3 formed on the casing sectionsand into the nuts 3 The pressure exerted by said bolts is sufiicient tobring the engaging flat faces of the casing sections into intimatecontact so that the easing is imperforate in this region and throughoutthe entire circumference of the casing which is desirably cylindrical.The mating surfaces brought together by bolts 3 should be flat and maybe ground so if desired before being put together. A film of cement,such as Bakelite varnish, is desirably applied to these flat surfacesbefore placing them together and tightening bolts 3. The circuitcontrolling element is within the casing and is operable to on and offpositions by suitably moving the casing which is desirably rotativelymounted upon a shaft 2 that is coaxial with the casing for this purpose.This circuit controlling element includes. as shown in the embodiment ofthe invention illustrated, a control tube or conduit 4 of refractoryheat resisting insulating material, preferably porcelain produced by thewet process. This tube or conduit is surrounded by a reenforcing metalcollar or jacket 5 that is preferably of iron and is initially ofsmaller internal diameter or size than the portion of the conduit itsurrounds and requires expansion by heat in order that it may be tightlysecured in place about conduit 4, the jacket -being allowed to cool andcontract tightly upon the conduit to provide the reenforcement desired.A circular clamp 6 having ears 6 is placed over both tube 4 and jacket5. Said ears 6' are securely fastened by a screw 7 passed therethroughinto a metallic supporting rod or insert 7 that is embedded in but doesnot pass through casing section 2 in the process of moulding this casingsection. anchored end sov as to be firmly gripped by the Bakelite andprevented from turning. Screw 7 not only tightens and fastens clamp 6about jacket 5 and conduit 4 but it immovably secures and supports theentire assembly of conduit 4, jacket 5, and clamp 6 on the insert 7which is of a length to support the entire assembly at a suitabledistance from the walls of the container and This rod is desirablyknurled at its generated within conduit 4 passes by direct conductionthrough the rod 7 and other metallic parts. As rod 7 is quite long andradiation within the casing from the surface of jacket 5 and clamp 6 aswell as from the surface of rod 7, itself, cuts down the temperature ofthe metal in this rod, a destructivelyhigh temperature is never attainedfor that portion of it which is embedded within the bakelite.

If desired, jacket 5 may be omitted and the circular clamping band 6used as the supporting and reenforcing member for conduit 4, but jacket5 is preferred due to its firmer grip upon the conduit.

The bore of conduit 4 communicates with the bore of an L shaped metallicfeed tube 9, preferably of iron, which fits snugly into an enlargementof the lower end of the conduit core. When in the normal circuit closingposition of thecontroller, as shown in Figs. 1, 2 and 3, feed tube 9constitutes the lower electrode of the device. Current enters thiselectrode from a lower metallic lead-in stud 10 about which the casingsection 2 is so moulded that this stud is fixed with respect to andextends through the casing and has around it bosses 10 that effectivelyseal the stud in its passage through the casing wall and strengthen suchcasing where the stud passes therethrough. A metal clamp 11 is securelyand fixedly mounted on the inner end of stud 10 by a screw 12 whichpasses through clamp 11 and into this stud. This clamp has ears 11 whichrespectively engage the legs of the L shaped feed tube 9. The stem ofmetallic screw 12 is positioned against the inner side of the bight offeed tube 9 to hold the tube against the clamp ears 11' and the head ofthis screw holds the feed tube against the body of clamp 11. Thisarrangement affords adequate electrical contact between the metallicstud 10 and the metallic feed tube or electrode 9.

The upper end of the bore of the conduit 4 is enlarged to form a well 13adapted to receive the spoon shaped end 14 of the upper metallicelectrode 14, which conforms to the well 13 and contacts with themercury 15 or other liquid conductor contained in the conduit bore andthe well enlargement 13 when the device is in circuit closing position.Slight clearance desirably intervenes between the w 11 of well 13 andthe electrode part 14'. pper electrode 14 is positioned independently ofconduit 4, being fastened in position upon a metallic lead-in stud 16 bya screw 17 threading into the inner end of this stud. Bosses 16'constituting parts of casing section 2 are securely moulded about theknurled end of stud 16 which is thus firmly mounted in the casing butdoes not pass therethrough.

' The lead-in studs 10 and 16 are shown with annular channels 10 and 16in addition to the usual knurling to further secure anchorages for thestuds and to provide longer, tighter and more diflicult'leakage pathsfor the diffusion or'leakage of air or gas there- 'along. The spoonshaped end 14 of the upper metallic electrode 14 has sufliciently fullcontact witht-he liquid conductor in the well 13 without substantiallyobstruct-' temperature might otherwise strike the casing wall forciblywith injurious effect. Said shield or barrier 14 also absorbs most ofthe heat contained in the liquid conductor and vapor striking it, sincebeing a metal, it has a relatively large heat absorbing capacity thatacts to condense the liquid conductor vapor and has a marked eflect inquenching any are which might arise between the electrode 14 and otherparts of op posite electrical polarity in the casing. Electrode 14 ispreferably made of copper or other metal of high electrical and thermalconductivity but plated with a mercuryresisting substance such as ironor nickel. The other metals exposed in the container to the action ofmercury or mercury vapor may also be made out of non-ferrous metal suchas copper, if such metal is coated with iron or other mercury resistantmetal.

Mating projections 19 and 20 are respectively integrally moulded withthe casing sections 1 and 2, and form, with contiguous portions of thecasing, a funnel-shaped space 21. The receiving end of the tubularelectrode or feed tube 9 may be freely received within the stem of thefunnel to virtually constitute a. continuation thereof. Said funnel andthe conduit 4 are so positioned with respect to the casin that, when thedevice is turned from on to 0d position, the mercury will be dischargedfrom the conduits 4 and 9 and the well 13 into the surrounding space andto an extent to open the circuit at 14, the liquid conductor thenfalling to the then bottom of the casing as indicated at 22 in Fig. 4.When the device is turned from off to on position, the cup of funnel 21will gather most of the liquid conductor at 22, this gathered liquidpassing by gravity through the cup and stem of the funnel and into thefeeding tube or hollow electrode 9 and the bore of conduit 4 and wellcontinuation 13 of the conduit borewhereby the circuit is closed at theelectrode tip 14', Figs. 1, 2 and 3. To insure closure of the circuit, Iprovide an excess of mercury or liquid conductor which finds lodgment inthe then bottom of the casing as indicated at 22 in Fig. 3, this excessflowing from the well when the device has been fully brought to its onor circuit closing position.

I have shown no means of limiting the movement of the casing and theenclosed switch to a range between the on and off positions as such mayobviously be employed and located as desired.

Current of the circuit to be controlled is supplied to the devicethrough leads 23 and 24 which are preferably flexible to permit propermotion of the device and which are fastened to the res ective lead-instuds 10 and 16 by means of binding screws 23' and 24'.

When the device is in the on position, and the controlled circuit isclosed at a lamp or other translating device, the circuit is inclusiveof the flexible lead 23, lower lead in stud 10, metal feed tube clamp11, metal feed tube and hollow lower electrode 9, the liquid conductor15 in the bore of the conduit 4 and well 13, the upper electrode 14, theupper lead-in stud 16 and the flexible lead 24.

An interiorly threaded sealing boss 25 is preferably provided in thecasing, this boss having a normally sealed bore which may be opened toaflord passage into and out of the casing when desired. Normally thiscasing is sealed or, in effect, imperforate throughout. A sealing screw26 may be employed to normally close the bore of boss 25 and therebycomplete the sealing of the entire casing or container from theadmission of air. Except for the liquid conductor, the device is firstassembled completely and the cement or varnish seal between the twomating casing halves 1 and 2 allowed to dry. During the drying processsealing screw 26 is removed, thus allowing access of outside air to theinterior of the casing to facilitate the drying. Sealing screw 26 isthen applied whereafter the entire device may be immersed for a shortinterval in a suitable sealing var- I nish in a tank under heavypressure. This pressure drives small globules of such varnish or sealingcompound into any pores in the casing that remain unfilled. The casingmay then be removed from the impregnating tank, sealing screw 26 againremoved and the varnish again allowed to dry, thus effectivelycompleting the sealing up of the pores last remaining unfilled. Afterthe final drying, the air in the casing is exhausted through the bore ofsealing boss 25, whereafter nitrogen, hydrogen, or other suitablenon-oxidizing gas is passed into the casing through this bore to takethe place of the exhausted air. The required amount of liquid conductoris now introduced through the boss whereafter the sealing screw 26 ispermanently screwed in place, sealing varnish having first been appliedto its threads. My experiments have shown that a casing of bakelite thusequipped provides a seal which will so minimize the diffusion of theoxygen of the outer air into before the mercury therein is depleted byoxidation to a suflicient extent to require its renewal or interferewith the successful operation of the switch. 7

As illustrated, the metal parts such as reenforcing metal jacket 5 andcircular support clamp 6 are so related asto prevent arc ing between theelectrodes from occurring around the outside of insulating conduit 4rather than through its bore. To assure this result, I make theoutside'diameter of insulating conduit 4 large as compared with thediameter of its bore. In one preferred form designed for nominal 115volt circuits, such outside diameter of insulating conduit 4 is Papproximately one inch, giving nearly a one half inch radius through theconduit from any portion of the electrically alive liquid conductor tothe metal of jacket 5 and clamp 6 and an even greater distance measuredover the surface of the conduit. Jacket 5 and clamp 6 surround conduit 4but are spaced from its electrode receiving ends sufficiently toinsulate said jacket and clamp from both electrodes. Moreover thecreepage or arcing spacing around th conduit 4 is divided into two gapsin series, one gap being at each end of such conduit, and this aggregatespacing is greater than the distance through the bore of said conduit.Because of such construction and spacing as well as the generous size ofthe conduit 4, undesired arcing cannot occur, even though small cracksor flaws may occur in the porcelain of the conduit 4 itself which mighttend to connect either electrode by way of the liquid conductor forcedinto such cracks to the exterior metal reenforcement of the tube. Itshould also be noted that any cracks or flaws developing in theporcelain cannot enlarge due to the metal reenforcement of the conduitand consequently would be almost microscopic in cross section. Anymercury forced into any such cracks would therefor have a negligiblecurrent-carrying capacity and negligible effect on the predetermined orrated current-carrying capacity of the device. Experiments prove thatthe bore of conduit 4 when such conduit is fashioned of preferredmaterial such as wet process porcelain is not marred to more than anegligible degree by the destructive action of arcing occurring upon thebreaking of current at commercial distribution potentials ofapproximately 15, 230, or 460/volts, the length of the column of liquidconductor in the bore 10 between electrodes bein kept above a certainminimum. I have iscovered that this minimum distance above whichdestructive arcing does not occur within the conduit bore upon thebreaking of such current either by manual or automatic operation of thedevice is of an inch for 115 volts and somewhat greater distances,although not proportionately greater. for the higher voltages mentioned.I attribute this action to the fact that upon the opening of the circuitthe resultant arc is confined to the small cross sectional area of theconduit bore and that above the critical arcing distance the circuitvolta is not suflicient, except for an exceeding y small period of timeto possibly sustaln arcingaround the conduit 4. Because of the shortford a commercially acceptable limit to the.

interval of time required for the circuit controller to automaticallyopen the circuit under predetermined standard conditions of overload.The hottest spot in the circuit controller is the liquid conductor inthe bore of conduit 4, heat flowing outwardly from this spot to theouter surface of the casing and being thus conducted and radiated away.This escaping heat reaches the external surface of conduit 4 through theporcelain of the conduit and flows into and through jacket 5 and clamp 6and into rod 7. Such heat is also radiated and conducted from the outersurface of the aforesaid parts to the gas filling the otherwiseunoccupied portion of the casing interior and from thence to and throughthe casing to be dissipated from its exterior surface. Rod 7 alsotransfers heat to the casing at the point where it is moulded and heldinto the same. The escaping heat also flows, by way of the electrodes,into and through the lead-in studs and into and through the casing atthe point where said studs are cast into the casing.

It is also radiated and conducted from the.

surface of the electrodes and lead-in studs to the gas filling of theinterior of the casing, from thence to and through the casing gall to bedissipated from its exterior surace.

For a predetermined length and crosssection of bore, any increase in thetotal heat conductivity of the aforementioned heat paths increases thelong-time current-carrying capacity of the controller because it enablesheat to be conducted away fromthe bore of conduit 4 to the exterior at agreater rate without the liquid conductor in such bore exceeding itsboiling or rupturing tem perature.

The long-time current-carrying capacity may be considered as the valueof the maximum sustained current which the controller will carry for anindefinitely extended interval. The short-time current may be consideredas the value of current required when applied to the controller,starting at room temperature, to produce an automatic interruption in agiven short-time interval, usually one minute. The ratio of short-timecurrent to long-time current may be considered as an indicator of thetime-lag of the device on overload. When the ratio is large, the timelag is large and the controller is slow in opening the circuit. When theratio is smaller, and approaches unity, the timelag is small andthecontroller is fast in opening the circuit.

In the preferred construction of my invention, upper electrode 14 has anextension or radiating fin 14 which fin, together with shield 1&radiates heat from the electrode surface to the gas in the interior ofthe container and increases the resultant heat conductivity for theescaping heat by way of this electrode. Such conductivity is alsoassisted by the large cross-section of the electrode in a directionnormal to the prevalent heat flow,-a cross-section which is greatly inexcess of that really needed for actual electrical conductivity in theelectrode. Tt is obvious that metal support clamp 11 with its ears 11'actually'aids in procuring the desired result and may be enlarged in itssize and surface area if desired for this purpose. The escaping heatwhich passes through the porcelain l encounters the jacket 5 and clamp6. These latter parts have a greater heat conductivity than theinsulating material of the conduit 4:. The heat is therefore, moreeasily conducted and radiated to the gas filling the casing interior bythe relatively large surfaces of these parts. Ears ii also conduct heatrapidly to supporting rod 7 and to the casing wall. By these means, thelongtime current for a predetermined length and cross section of bore isincreased. Without them, it is inherently smaller. Shorttime current,however, is largely unafilected by such means.

Heat generated with short-time current flowing tends to spread out andescape to the exterior of the casing but before it can penetrate morethan a small distance from where it is formed within bore of conduit 4,the circuit is interrupted. Short-time current is mainly aflected by thecross section of such bore. It is also affected by the heat storagecapacity and heat conductivity of the liquid conductor in the boreitself and a zone or layer of material immediately surrounding thebore,also, to an extent, by the length of bore. It is only slightlyafiected by thermal characteristics of the electrodes, in-

sulating conduit and its support and the casing at any distance from theactive or hot portion of such bore. Long-time current values can,therefore, be increased or decreased by employing the means describedfor increasing or decreasing escape of heat from the hot spot of thecontroller and without substantially altering the value of theshort-time current. The ratio between invention, suitably designed, itis possible to shorten this naturally excessive time lag to particularfor one controller having a long time current carrying capacity inexcess of forty amperes l have secured a ratio of short time capacity tolong time capacity (on a one minute interval basis) of less than 1.20 incontrast to a. commercially acceptable ratio of about 1.36. Thecircuit-controlling element shown in Fig. 8 is slightly modified to showhow the increase of heat conductivity from the bore outward may beeffected. The metal ring of jacket 5 at about the midpoint out theinsulating conduit 4 is enlarged in the shape of a. metal band 5' whichis substantially integral with jacket 5 but which may be inserted in anannular groove left for it in the porcelain before jacket 5 is applied.This metallic band 5 extends inward toward the hot spot in bore 15 andis of almost any commercially desired value. In

tions 5 on each end of the. jacket 5 are 7 crimped down over an annularshoulder near each end of conduit at after Such jacket is applied to theconduit. The conduit 4 is thus given some longitudinal reenforcementagainst fracture by jacket 5 that supple-.

ments the radial reenforcement normally effected by this jacket. In theconstruction shown in Fig. 9 the clamping ears 6' for the support of theconduit 4 and jacket 5 are fastened directly to and made enlargements of'acket 5 as by welding.

hanges may be made without departing from the invention.

Having thus described my invention, I claim:

1. An electric circuit controller including a casing; a conduit ofheat-resisting insulation within the casing; a liquid conductor withinthe bore of the conduit; electrodes connectible by the liquid conductor;and metal supporting means within the casing and electrically insulatedfrom the electrodes for fixedly supporting said insulating cons duitwithin the casing. v

2. The structure of claim 1 wherein the supporting means for theinsulating conduit is fastened securely to a wall of the casing.

3. An electric circuit controller including a casing containing aquantity of liqud conductor; and control tube, two electrodes capable ofbeing connected by such liquid conductor when in said control tube, oneof such electrodes being bent and tubular and communicating with saidcontrol tube; a lead-in stud fastened firmly in the casing wall; andmeans for fastening the tubular electrode to said stud.

4. An electric circuit controller including a casing forming a chambertherewithin; electrode within the casing; a liquid conductor within thecasing connecting the electrodes when desired; lead-in members for thecurrent in the circuit to be controlled moulded into and through thecasing wall, said casing being moulded of an insulating material andcomprising two parts having mating surfaces; and means entirely exteriorof said chamber for clamping said surfaces together.

5. An electric circuit controller including a casing; a conduit ofheatresisting insulation within the casing; a liquid conductor withinthe bore of the conduit; electrodes within said casing connectible bysaid liquid conductor; and a metal shield on one electrode and oppositeone end of the bore of said conduit to receive impact from hot gasesexpelled from the conduit to protect the electric circuit controllerincluding a casing; a conduit of heat-resisting insulation within thecasing and mainly s aoed substantially therefrom; a liquid con uctorwithin the bore of the conduit; electrodes connectible by said liquidconductor; and means having a greater thermal conductivity thanthe'thermal conductivity of the inshield wit sulating material of saidconduit and so applied to the exterior of such conduit as to assist inthe conduction of heat from the bore of said conduit to the exterior ofthe casing.

7. An electric circuit controller including a casing; a conduit ofheat-resisting insulation within the casing and mainly spacedsubstantially therefrom; a liquid conductor within the bore of theconduit; and electrodes connectible by said liquid conductor, one ofthese electrodes having a heat radiatmg portion positioned out of theline of the predominating path of electrical current flow in theelectrode.-

8. An electric circuit controller including a casing; a conduit ofheat-resisting insulation within the casing and mainly spacedsubstantially therefrom; a liquid conductor within the bore of theconduit; and electrodes connectible by said liquid conductor, one of theelectrodes having a portion unessential to the flow of current throughthis electrode, and serving to enlarge the heatconductmg capacity ofthis electrode for heat flowing from-the conduit bore to the exterior ofthe casing.

9. An electric circuit controller including a casing; a conduit ofheat-resisting insulation within the casing; a liquid conductor wlthinthe bore of the conduit, this bore be inclusive of a well at one end forholdmg 'quid conductor; and electrodes connectible by said liquidconductor, one of said electrodes ha a s n-sha ti that extends intowell. P

10. An electric circuit controller including a cas1ng; a conduit ofheat-resisting insulation within the casing; a liquid conductor withinthe bore of the conduit; electrodes connectible by said liquidconductor; and. an anchoring member mainly sup rtmg said conduit andcarried by a wall of the casing and insulated from said electrodes.v

11. An electric circuit controller including a casing; a conduit ofheat-resisting ination within the casing; a liquid conductor within theconduit bore; electrodes connectible b said liquid conductor; and a thecasing and opposite one end of the conduit bore to receive impact fromhot gases expelled from the conduit to protect the casing.

12. An electric circuit controller including a casing; electrodes withinthe casing; a liquid conductor within the casing adaptable to connectthe electrodes; lead-in members for the current in the circuit to becontrolled moulded into and through the casing wall, said casing beingmolded of an insulating material and comprising two parts having matingsurfaces; a cement-like material between said mating surfaces forsealing and holding them together, and a control tube mating surfacesand one of which-parts is of moulded insulating material; and acement-like material between said mating surfaces for sealing andpermanently holding them together; said control tube having a terminedmaximum current without interrupting the circuit. K

14. An electric circuit controller comprising a casing movable to oiland on positions; a control tube within the casing; a liquid conductorwithin the casing, a feed tube for collecting liquid conductor from thecasing and conveying it into the control tube as the casing is movedfrom off to on;

3 a supporting member for the control tube to hold it in spaced relationto a wall of the container, the bore of said control tube beinginclusive of an enlarged portion at the end opposite the feed tube; andan electrode exposed to make contact with liquid conductor in saidenlarged portion of the control tube bore; said electrode being soshaped and spaced within said enlarged portion as to form a passagecommunicating with said 40 bore and said container andproviding a freedischarge port from the control tube to the container.

' 15. An electric circuit controller, comprising a casing movable to.oil and on po- 4 sitions; a control tube within the casing; a liquidconductor within the casing; a metal feed tube for collecting liquidconductor from the casing and conveying it into the control tube as thecasing is moved from off to on; a supporting member for the control tubeto hold it in spaced relation to a wall of the container," the bore ofsaid control tube being enlarged into a well at the end opposite thefeed tube, and an electrode dipping into the liquid conductor in saidwell.

16. A control tube of insulating material for a circuit controlleremploying liquid conductor, said tube having a bore calibrated to themagnitude of current which it is desired to control, ametal jacketsurrounding a portion of said tube and metal means surrounding said tubeand extending inwardly from the outside of the tube toward bore of suchcaliber as to carry only a prede-V its bore for the purpose of rapidlyconducting heat generated within the bore to the outer surface of thetube.

17. A control tube of insulatingmaterial for a circuit controlleremploying liquid conductor, said tube having a bore calibrated to'themagnitude of the current which it is desired to control and metal meansassociated with said tube and placed in a reduced portion of the outsideof said tube, said metal means serving to rapidly conduct away a portionof the heat generated within said bore.

18. A control tube of insulating material for a circuit controlleremploying liquid conductor, said tubehaving a bore calibrated to themagnitude of the current which it is desired to control and metal meansassociated with said tube and placed in a reduced portion of the outsideof said tube approximately even with the center of the bore, said metalmeans serving to rapidly conduct away a portion of the heat generatedwithin said bore.

19. An electric circuit controller including a casing; a conduit ofheat-resisting insulation within the casing; a liquid conductor withinthe bore of the conduit; electrodes connectible by said liquidconductor; and a separable metallic anchoring member mainly supportingsaid conduit, carried by a wall of the casing and insulated from saidelectrodes.

20. An electric circuit controller including a conduit assembly formedmostly of heat-resisting insulating material but including a reinforcingmetallic band, a liquid conductor within the bore of the conduit,electrodes connectible by the liquid; conductor, and a casing enclosingsaid elements and leaving around them a space for expansion of themercury into vapor; the length of said bore between electrodes being atleast seven-sixteenths of an inch and the shortest distance which wouldbe traversed by a current such as an are between said band and one ofsaid electrodes being approximately seven-sixteenths of an inch.

21. An electric circuit controller including a conduit assembly formedmostly of heatresisting insulating material but including a reinforcingmetallic band, a liquid conductor within the bore of the conduit,electrodes connectible by the liquid conductor, and a casing enclosingsaid elements and leaving around them a space for expansion of themercury into vapor; the length of said bore between electrodes being atleast seven-sixteenths of an inch and the shortest total distance whicha current flowing from one electrode to the other through the band wouldhave to jump by arcing being at least seven-sixteenths of an inch.

STANLEY S. GREEN.

